“Herpes virus” comes from the ancient Greek meaning “to creep or crawl while hiding itself.” The feature of this virus is that once it has infected patients, the virus continues to hide in their ganglia even after symptoms have dissipated, and becomes active again upon reduction of the patients' immunity.
At present, 8 types of herpes viruses are known to infect humans: herpes simplex virus type 1 (HSV-1) which causes gingivostomatitis, keratitis, pharyngitis, herpes labialis, etc.; herpes simplex virus type 2 (HSV-2) which is responsible for genital herpes infections; varicella-zoster virus (VZV); cytomegalo virus (CMV) which causes retinitis, hepatitis, interstitial pneumonia, etc.; EB virus (EBV) which is responsible for infectious mononucleosis; human herpes virus 6 (HHV-6) which causes exanthema subitum; human herpes virus 7 (HHV-7); and human herpes virus 8 (HHV-8) which is responsible for Kaposi's sarcoma seen in AIDS patients.
Herpes virus infections are characterized by persistent infection (latent infection) in the body (mainly in ganglia) following primary infection. Except for VZV and HHV-6 cases, primary infection is often inapparent infection. After primary infection, regardless of whether it is apparent or inapparent, the viruses establish latent infection in trigeminal and/or sacral ganglia, and they further cause blisters at specific skin sites such as areas around the lips and genitals (recurrent infection) when the viruses become active again due to fatigue, pregnancy, injury, febrile diseases and other causes.
The incidence rate of herpes zoster is reported to be 300 patients per year per 100,000 adults. Herpes zoster patients are numerous particularly among the elderly (50 to 79 years old), and tend to slightly increase. In recent years, there has been an increasing number of patients who develop herpes zoster at younger ages and repeatedly. In patients whose pain persists for a month after developing the disease, the pain disappears within 3 months in half of such patients, but it persists for 3 months or longer in the remaining half of the patients, 20% of which will have pain persisting for longer than a year (postherpetic neuralgia).